This project focuses on essential proteins from three major global pathogenic protozoa, Trypanosoma brucei, Trypanosoma cruzi and Leishmania species. These are related parasites which cause sleeping sickness, Chagas disease, and leishmaniasis, respectively, and are responsible for tens of millions of infections annually, mainly in the tropical and subtropical areas of the world. These sophisticated protozoa are able to avoid the host defense systems, and cause prolonged suffering for the patients. The few drugs that are available have serious side-effects and drug resistance problems are rising. This proposal addresses the need for developing new therapeutics by targeting a critical biological pathway shared by these eukaryotic organisms. This strategy will facilitate drug development across the three protozoa by using the same inhibitor scaffolds. Specifically, three aminoacyl-tRNA synthetase (aaRS) families that are essential for protein synthesis in living cells will be targeted by integrating structure-based and compound library screening methodologies. The approaches include: (i) piggyback inhibitor development based on known aaRS inhibitors for other pathogens (some of which inhibit trypanosomatids several orders of magnitude better than human cells), (ii) high throughput solution screening of chemical libraries, (iii) fragment cocktail crystallographically, and (iv) computational chemistry. Compound hits will be subjected to rounds of optimization to improve potency and selectivity by structure-based design. Newly synthesized inhibitors will be evaluated by enzyme and cell-based assays to assess efficacy, selectivity and toxicity. The goal of this project is to arrive at one or two submicromolar inhibitors for five of the aaRS enzymes targeted. These would provide new starting points for subsequent drug development efforts.